The present invention relates to a method for securely determining the position of an object moving along a course which is known by the location device.
The term “course” is intended to mean a subset of the space delimited by a tubular surface of arbitrary and variable cross section, in which the vehicle is strictly constrained to move. In the event that the cross section of this tube can be neglected, this gives two equations linking longitude, latitude and altitude of the moving object.
The present invention relates more precisely to a method for determining the location of a train moving on a railway track of which the exact path is known.
The present invention relates to a method for determining the location and/or the positioning of a vehicle in terms of railway transport security. It involves being able to determine in a quasi-instantaneously way and with a given probability the location of a vehicle moving on a known course, or more precisely the zones of non-presence of said vehicle on a section.
In railway signalling, a train is not allowed to enter a specific section of track until it is certain that the train in front has departed therefrom, i.e. the track section in question is free. To that end, it is necessary to ascertain with a predetermined, extremely small margin of error (for example with a maximum error level in the order of 10−9 and preferably in the order of 10−12) the zones in which non-presence of a train can be relied upon, and to do so at each iteration of the calculation.
It is known to determine the precise location of a vehicle, and in particular of a train, with trackside detection devices (track circuits, axle counters, . . . ) for train detection purposes.
It is also known to use train borne train position determination systems for fail safe train control purposes. These train position determination systems are based on train borne sensors (wheel sensors, radars, . . . ) which give the relative position of the train with reference to trackside location materialised by trackside installed beacons (or equivalent devices). These trackside reference points are required because of the nature of the applied sensors, in order to allow resetting the error accumulated by the train location system over time (radars) and/or distance (wheel sensors).
Those solutions have important impact on the life cycle cost of a train control/command system:                Trackside detection systems have important acquisition, installation and maintenance cost, due to the quantity of equipment to be installed and their connection by cable to an interlocking system.        Existing train borne solutions, based on wheel sensors and/or radar sensors also have important acquisition, installation and maintenance costs, mainly due to their location as they are mounted below the locomotive.        
The position of a vehicle can be determined using a satellite communication system by means of a GNSS (Global Navigation Satellite System) like GPS, GLONASS, and the future Galileo system. WO 02/03094 discloses a method for secure determination of an object location, preferably a vehicle moving along a known course. This method takes advantage of the deterministic trajectory of the train to reach an optimal compromise between safety, availability and accuracy. However, this system cannot provide a higher accuracy where needed, e.g. near stations or crossings.
EP-0825418 A2 discloses the use of several sensors to determine the position of a train. Data relating to position and error interval from several sensors, comprising beacons and GPS, is used to determine the position of the train. However, this system implies a calculation involving severals operations including integration. It is therefore considered as complex.